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Biomedical subjects

N L Oleinick

Publications and source records attributed to N L Oleinick.

At least 91 records · Page 5Linked to original sources
PubMed1979

Selective inhibition of precursor incorporation into ribosomal RNA in gamma-irradiated Tetrahymena pyriformis.

Sublethal doses of gamma radiation are known to inhibit total RNA synthesis in the ciliate protozoan Tetrahymena. To determine if the synthesis of a particular class of RNA is preferentially inhibited, pulse-labeled RNA was isolated from normal exponentially growing cells, irradiated cells, and cells in which total RNA synthesis had recovered to the pre-irradiation level. The RNAs were analyzed by SDS-polyacrylamide gel electrophoresis and oligo(dT)-cellulose column chromatography. Inhibition of RNA synthesis primarily involves ribosomal RNA. However, radiation does not cause a delay in the processing of precursor rRNA or a preferential loss of either of the mature rRNAs. Following irradiation, poly(A)-containing RNA [poly(A+)RNA] is synthesized at a rate up to three times greater than the control rate. The elevated poly(A+)RNA synthesis occurs during the period of depressed rRNA synthesis and even after rRNA synthesis has recovered to its pre-irradiation rate. While the sizes of the total cellular ribonucleoside triphosphate pools are depressed in the irradiated cells, these pools probably do not represent the actual compartments containing the precursors for RNA synthesis, and the observed changes cannot explain the modifications in macromolecular synthesis in irradiated Tetrahymena.

Gamma Rays↗
PubMed1979

The initiation and elongation steps in protein synthesis: relative rates in Chinese hamster ovary cells during and after hyperthermic and hypothermic shocks.

The relative rates of the initiation and elongation phases of protein synthesis have been determined in heat- and cold-shocked CHO cells from measurements of the incorporation of 35S-methionine into N-terminal and internal positions of growing peptides by a modified Edman degradation. When the cells are shifted from 37 degrees C to temperatures between 10 degrees C and 34 degrees C, the rate of initiation is at first reduced more extensively than that of elongation. After 20 to 30 minutes at the lower temperature, however, the cells undergo a metabolic adjustment which includes increasing the rate of initiation until it corresponds to the rate of elongation at that temperature. Calculated apparent energies of activation for initiation and elongation are in reasonable agreement with those determined in other mammalian cells. When the cooled cells are returned to 37 degrees C, the rates of initiation and elongation recover immediately but do not exceed the control values. Exposure to elevated temperatures (43 degrees C) causes an immediate cessation of initiation and thus a delayed inhibition of elongation; upon return to 37 degrees C, the rate of initiation is transiently elevated above the control rate, and the rate of elongation returns to the control rate after a 2- to 3-minute delay. Hence, a factor which leads to supranormal rates of initiation may accumulate at high but not at low temperatures.

Cell Line↗
PubMed1979

Radiation-induced fluctuation of the polysome content in adequately oxygenated tetrahymena pyriformis.

The polysome content of the ciliate protozoan Tetrahymena pyriformis is transiently reduced by gamma-irradiation. In order to test whether this is a result of a respiration-produced or radiation-produced hypoxia or some other mechanism, the oxygen content of the culture was determined during and after irradiation, and the polysome contents and rates of amino acid incorporation were measured with and without air bubbling. Irradiation (40 krad at approximately 3 krad/min) produced approximately a 25 per cent loss in dissolved O2 content in the medium. This decrease is not sufficient to affect the polysome level, since (a) the same radiation-induced loss of polysomes and inhibiition of amino acid incorporation was observed whether or not the culture was bubbled with air during the irradiation and (b) bubbling unirradiated cultures with gas mixtures containing as little as 17 per cent of the normal O2 content did not influence the polysome level. As long as the cells are irradiated as a shallow layer in open flasks, replacement of O2 from the gas phase appears adequate, and neither respiration-induced nor radiation-induced hypoxia masks the effects of the radiation.

Amino Acids↗
PubMed1975

Radiation-induced inhibition of RNA synthesis in Tetrahymena pyriformis.

Radiation-induced disturbances in RNA synthesis were investigated in exponentially growing Tetrahymena. Sub-lethal doses of gamma-radiation lead to a transient, dose-dependent decrease in the rate of total RNA synthesis measured by 3H-uridine incorporation, without an alteration of 3H-uridine uptake by the cells. The rate of 3H-uridine incorporation decreases exponentially with dose. In contrast, the duration of inhibition of RNA synthesis is linearly dependent on dose. Target-theory calculations suggest that the sensitive molecule has a molecular weight of about 2 X 10(7) Daltons.

Animals↗